1. Field of the Invention
The present invention relates to a semiconductor apparatus used mainly as a switching device in, for example, a motor drive device in an inverter, an AC servomotor, an air conditioner, etc., or a power supply device in a vehicle, a welding machine, etc., and more specifically to the improvement of an electrode wiring structure in a semiconductor apparatus applicable as a power semiconductor module.
2. Description of the Related Art
Normally, a semiconductor module can be, for example, a plurality of semiconductor devices (semiconductor chips) connected in parallel to have a larger current capacity, a simple circuit of several types of semiconductor devices, semiconductor devices into which a drive circuit is incorporated, etc.
FIG. 1 is a plan view of an example of a conventional power semiconductor module.
In the semiconductor module shown in FIG. 1, an insulated substrate 2 is mounted on a base plate 1 for fixing. On the insulated substrate 2, a plurality of (four as an example shown in FIG. 1) semiconductor devices (semiconductor chips) 4 are mounted in series through a conductive plate 3. In this example, the semiconductor device 4 is a MOSFET (metal oxide semiconductor field-effect transistor) having a source electrode and a gate electrode on the top side, and a drain electrode on the reverse side.
The conductive plate 3 is electrically connected commonly to the drain electrode of each semiconductor device 4 by mounting the semiconductor device 4 directly on it, thereby functioning as a drain electrode of the entire module. On the insulated substrate 2, a source electrode 5 and a gate electrode 6 of the entire module are mounted along the array of the semiconductor devices 4 and on either side of the conductive plate 3.
The source electrode 5 is electrically connected commonly to the source electrode of each semiconductor device 4 through a wire (bonding wire) 7, and the gate electrode 6 is electrically connected commonly to the gate electrode of each semiconductor device 4 through a wire (bonding wire) 8. A gate resistor such as a silicon chip resistor, etc. can be provided on the gate electrode 6, and the wire 8 can be connected thereto.
Furthermore, a drain terminal 9 is led outside the module as an external terminal from a portion of the conductive plate (drain electrode) 3, a source terminal 10 is led outside the module as an external terminal from a portion of the source electrode 5, and a gate terminal 11 is led outside the module as an external terminal from a portion of the gate electrode 6.
Although not shown in the attached drawings, the entire module is normally put in a resin package, and the space in the package is filled with gel or epoxy resin, etc. The above mentioned external terminal is drawn in a two-dimensional array in FIG. 1, but it is appropriately bent and exposed on the top or side of the package.
The semiconductor module with the above mentioned configuration has a plurality of semiconductor devices 4 connected in parallel between the drain terminal 9 and the source terminal 10. Therefore, in principle, the main current flowing between the drain terminal 9 and the source terminal 10 can be controlled by applying a control voltage between the gate terminal 11 and the source terminal 10, and simultaneously setting all semiconductor devices 4 ON/OFF.
In the conventional semiconductor module as shown in FIG. 1, restrictions are placed by the gate electrode 6 especially on the wiring pattern from the drain electrode (conductive plate) 3 to the drain terminal 9. That is, the drain terminal 9 is led outside through the path from the end portion of the conductive plate 3 without passing the gate electrode 6.
Therefore, the lengths of the current paths are entirely long as indicated by the dot-and-dash line as shown in FIG. 2 when the main current flows from the drain terminal 9 to the source terminal 10 through each semiconductor device 4, and the lengths are uneven depending on the position of each semiconductor device 4. Especially, the current path through the semiconductor device 4 shown in FIG. 1 on the right is considerably longer than the current path through the semiconductor device 4 on the left.
Since the inductance generated in the current path is substantially proportional to the length of the path, the inductance increases correspondingly when the current path is long as described above. As a result, the surge voltage generated when the semiconductor device 4 is turned off rises, thereby possibly destroying the semiconductor device 4.
In addition, when the lengths of current paths are not even, the wiring resistance also becomes uneven depending on the position of each semiconductor device 4. As a result, the current value becomes unbalanced, thereby leading excess current through only a part of the semiconductor devices 4, and also possibly destroying the semiconductor devices 4. Therefore, with the problem of the above mentioned excess current to a part of the semiconductor devices 4 has prevented the maximum current through the module from largely increasing.
Furthermore, with the drain terminal 9 directly connected to the conductive plate 3 to be mounted on the insulated substrate 2 as the semiconductor module as shown in FIG. 1, there can easily be a crack in the joint (the portion encompassed by a circle A indicated by a dot-and-dash line) between the drain terminal 9 and the conductive plate 3 due to the expansion and contraction by the heat from the semiconductor devices 4.
To prevent the above mentioned cracks, the drain terminal 9 can be connected through a plurality of wires (bonding wires) instead of directly connecting them. That is, in FIG. 1, the joint portion (indicated by the dot-and-dash circle A) can be separated and replaced with a plurality of wires.
With the above mentioned configuration, cracks can certainly be suppressed. However, the above mentioned problems of the lengths and unevenness of the current paths still remain unsolved. These problems become severer with an increasing number of semiconductor devices 4 mounted on one insulated substrate 2.
An object of the invention is to solve the above mentioned problems with the conventional technology, and to provide a semiconductor apparatus capable of not only suppressing cracks, but also shortening and leveling the lengths of the current paths, reducing a surge voltage, and improving the maximum current in the apparatus.
To attain the above mentioned object, the present invention has the following configuration.
That is, the semiconductor apparatus according to the present invention includes: a plurality of semiconductor devices mounted in one or more arrays on a substrate; a first main current electrode mounted along the array(s) of the semiconductor devices, and commonly connected to each of the plurality of the semiconductor devices though the substrate; and a second main current electrode mounted along the array(s) of the semiconductor devices opposite the first main current electrode through the mounting area of the semiconductor devices, wherein the substrate is connected to the first main current electrode through a plurality of wires arranged at equal (or substantially equal) distances along the array(s).
The substrate can be a conductive plate or a conductive layer mounted on an insulated substrate. However, it is obvious that other configurations can be accepted only if a path of the main current flowing from the main current electrode to each of the semiconductor devices can be provided.
The above mentioned main current electrode is a drain electrode or a source electrode when the semiconductor device is, for example, a MOSFET. It also can be a collector electrode or an emitter electrode when the semiconductor device is, for example, a bipolar transistor. Although the second main current electrode is to be directly connected to each of the semiconductor devices mounted on the substrate through wires (bonding wires), etc. On the other hand, the first main current electrode is to be indirectly connected to each of the semiconductor devices through the substrate. That is, it is to be connected to the substrate through the wires to form the current path of the main current from the first main current electrode to each of the semiconductor devices through the wires and the substrate.
According to the present invention, the first and second main current electrodes are respectively arranged along the array(s) of the semiconductor devices and on each side of the mounting area of the semiconductor devices, and the substrate is connected to the main current electrode through a plurality of wires mounted at equal (or substantially equal) distances along the array(s) of the semiconductor devices.
It is not always necessary that the plurality of wires are equally arranged, that is, arranged at equal distances, but they are to be arranged at substantially equal distances. For example, when a predetermined number (two, for example) of wires are arranged corresponding to each semiconductor device, they are not arranged at equal distances in the entire module, but in the range of the arrangement at xe2x80x98substantially equalxe2x80x99 distances.
With the above mentioned configuration, the first main current electrode is actually connected to the substrate through a plurality of wires. However, since the plurality of wires are arranged along the array(s) of the semiconductor devices, the first main current electrode is practically connected to the substrate directly on their sides (plane along the array(s) of the semiconductor devices). Therefore, the main current flows substantially straight from the first main current electrode to each semiconductor device through the substrate, and further to the second main current electrode.
Thus, since the current path of the main current is formed substantially straight from the first main current electrode to the second main current electrode regardless of the position of each semiconductor device, the current path can be considerably shorter, and is leveled. As a result, the inductance can be reduced, and the surge voltage can be suppressed, thereby leveling the main current flowing through each semiconductor device, and increasing the maximum current in the entire semiconductor apparatus (semiconductor module).
Furthermore, the first main current electrode is not actually connected directly to the substrate, but is indirectly connected through wires, thereby suppressing the generation of cracks in the joint portions due to the expansion and contraction of the semiconductor devices.
With the above mentioned configuration, it is desired that the wires connecting the first main current electrode to the substrate is shortest possible, but long enough to connect them.
Furthermore, it is desired that the first external terminal led outside from the first main current electrode and the second external terminal led outside from the second main current electrode are opposite each other through the mounting area of the semiconductor devices.
The present invention has a unique connection structure between the substrate and the first main current electrode, and the connection structure between the second main current electrode and each semiconductor device is not limited to a specific structure. However, it is desired that the entire current path from the first main current electrode to the second main current electrode is as straight as possible.